Andrew S. Nencka, PhD

Education

Research Interests

Image Acquisition Acceleration

One aspect of my research work has been to leverage the phase of acquired images, along with varying receive coil sensitivities, to further spatially encode the acquired data. With the assumption of real-valued images—an assumption often made for partial Fourier image reconstruction—this insight theoretically enables acceleration factors of 2N for an array of N coils. We have used this technology to implement a parallel slice acquisition method that simultaneously excites an array of slices with varying magnetization phase such that the magnetization phase and receive coil sensitivity profiles can be used to unalias the acquired slices. We have also used this technology to acquire and unalias accelerated single-slice images acquired with a single-channel body receiver coil.

Fast MR Relaxometry

Image acceleration techniques have enabled the development of a fast relaxometry pulse sequence, which we have named the gradient-recalled echo, asymmetric spin echo (GREASE) pulse sequence. The pulse sequence, including six echo-planar imaging readouts, two 90-degree excitation pulses, and two 180-degree refocusing pulses in each repetition, allows the computation of T1, T2, and T2* with each repetition. The acceleration techniques of GRAPPA and partial Fourier acquisition in the echo-planar imaging readouts reduce the duration of the imaging readout train so that signal decay does not eliminate the needed signal in later echoes. Thus, the relaxivity values for a single slice of 2 mm isotropic resolution can be acquired in less than 300 ms with this sequence. Further, the nearly simultaneous acquisition of the six images, the identical echo-planar imaging readouts, and the usage of the six images from each repetition for the estimation of relaxivity parameters allow the perfect coregistration of the computed maps.